It works,
RPi 4 with Waveshare 7.9 inch.
Don’t know why on the list of my outputs, the HDMI1 was active, along with DSI/ But I had no HDMI cable plugged. So, It did not work until I disable the HDMI with this userconfig.txt - nohdmi
dtoverlay=vc4-kms-v3d-pi4,nohdmi
dtoverlay=vc4-kms-dsi-waveshare-panel,7_9_inch
Touch Display V 3.4.0
- Support screen rotation from the menu